1. Field of the Invention
The present invention relates generally to plant growing methods and containers, and more particularly, to methods and containers for growing plants such as shrubs or trees in preparation for transplanting.
2. Description of the Prior Art
Trees and shrubs and other plants intended to be transplanted have for some time been grown above ground in bags or containers. Plants held in bags or containers can be grown at a faster rate than those grown in the ground, are more easily tended, and because the roots of the plants are not severed when the plants are transplanted, transplanting is less traumatic on the plant and is more easily accomplished.
With respect to trees and shrubs, it is often desired to grow the trees or shrubs in the ground until the tree or shrub is sufficiently large as to be commercially desirable for transplantation. At this point the tree is removed from the ground, care being taken to retain a ball of soil around the major root structures of the tree. The soil and roots are wrapped in burlap to retain the soil and roots in a transplantable condition and to allow roots to grow in the retained soil. The burlap wrapped trees are then placed together and the burlap balls are covered with mulch and sawdust to prevent drying. When transplanting to the soil is desired, the burlap covered root ball is placed in the ground and covered with soil. The burlap decomposes and the roots grow into the surrounding soil.
A problem with the burlap covered root balls is that the burlap prematurely decomposes and allows the root ball to fall apart. Further, the trees produce roots which extend through the burlap container out into the mulch or sawdust and these roots are lost during transplanting producing stress on the plant. Still further, use of the burlap covered root ball is untidy and not commercially as aesthetic for a nursery or the like.
Other than burlap bags, other devices have been used to retain the soil and roots of plants and trees prior to transplanting. These devices have included metal cans with holes punched in them and cylindrical or conical plastic containers. A problem with the cylindrical containers is that as roots grow downward within the containers, the round bottom of the container causes spiral root growth. Spiral root growth is damaging to the plant in that such root growth does not provide lateral anchorage for the plant when transplanted and the spiral roots do not extend into the soil to gather nutrients. Some containers have openings in the bottom to terminate the spiral root growth. When a root extends through an opening, it is air pruned and growth of this root stops.
Landscape plants have also been grown in square, bottomless containers placed on wire surfaces where roots reaching the bottom of the container are air pruned. However, most of the root tips produced end up at the bottom of the container, and the requirement of placing the containers on wire screen surfaces generally makes the practice uneconomical. Further, such open bottom containers are not easily moved without spilling or losing the growth medium contained therein.
More recently, containers have been developed for controlling spiral root growth whereby the root tips are physically trapped by surfaces in the container and are prevented from elongating or the circling root tips are caused to pass through vertical openings in the sides of the container whereby the tips are air pruned. An example of the root trapping type of container is described in U.S. Pat. No. 4,442,628 issued Apr. 17, 1984. An example of a container including vertical side wall openings for air pruning circuling roots is described in U.S, Pat. No. 4,497,132 issued Feb. 5, 1985. While such root trapping and air pruning containers have been utilized successfully, some spiral root growth still takes place and the development of lateral root growth and root tips has been less than optimum.
By the present invention an improved container for growing plants intended to be transplanted is provided whereby spiral root growth is prevented and the development of lateral root and branched root tips along and around the sides of the container is maximized. Particularly, the present invention is well suited for large plants such as trees and shrubs.